1. Field of the Invention
The present invention relates to a machine tool that machines a workpiece while moving a vertically set spindle and the workpiece relatively to each other in X-axis, Y-axis, and Z-axis directions.
2. Discussion of the Related Art
For example, a vertical machining center is generally structured, as shown in FIG. 5, to include: a column 61 fixedly disposed on a back end of a fixed bed 60 when seen from a front side of the machine; a saddle 62, for placing a workpiece W thereon, disposed on a front part of the fixed bed 60 to be movable in a Y-axis (forward and backward) direction; a table 63 disposed on the saddle 62 to be movable in an X-axis (right and left) direction; and a spindle head 65, with a spindle 64 attached thereto, disposed on a front face of the column 61 to be movable in a Z-axis (vertical) direction (see, for example, Japanese Patent Application Laid-open No. Sho 63-62636).
A driving system of a machining center of this type is generally structured such that, for example, as shown in FIG. 6 and FIG. 7, the spindle head 65 is movably supported by two guide rails 67, 67 and is driven by one ball screw 68 disposed between these guide rails 67. Note that 69 denotes a nut fitted to the ball screw 68, and 70 denotes a drive motor.